It is possible but highly unlikely that the drivers for the keyboard are corrupted or disabled.
Try this: Shutdown the machine and disconnect the keyboard cable from the back of the PC. Then reconnect the keyboard cable and power up the machine and try again to login. If this does not work, try the shutdown – startup procedure again. If the keyboard is still unrecognized, it may be the keyboard connection, or the keyboard itself, a hardware issue. Try another keyboard, if you still get the problem, it is not the keyboard, but could be the port for the keyboard on the PC, which if it is a modular port, could also be a motherboard issue. It is usually a process of elimination when it comes to troubleshooting hardware issues.